Heat-sensitive recording material

Abstract

A heat-sensitive recording material comprises a heat-sensitive layer which is applied onto a base and contains a color-producing substance, which is usually colorless or only slightly colored, and an activator which, under the action of heat, causes the color-producing substance to produce a coloration. In accordance with the invention, the heat-sensitive layer contains a sulfonic acid ester, in particular of a secondary alcohol, as the activator.

I claim: 
     
       1. A heat-sensitive recording material which comprises a heat-sensitive layer which is applied onto a base and contains a color-producing substance, which is usually colorless or only slightly colored, and an activator which, under the action of heat, causes the color-producing substance to produce a coloration, wherein the activator is a sulfonic acid ester. 
     
     
       2. A heat-sensitive recording material as claimed in claim 1, which contains, as the activator, an ester of an aromatic sulfonic acid. 
     
     
       3. A heat-sensitive recording material as claimed in claim 2, which contains, as the activator, an ester of benzenesulfonic acid and/or an ester of toluenesulfonic acid. 
     
     
       4. A heat-sensitive recording material as claimed in claim 3, which contains, as the activator, isopropyl toluenesulfonate, but-2-yl toluenesulfonate, butane-2,3-diol toluenesulfonate or hexane-2,5-diol toluenesulfonate. 
     
     
       5. A heat-sensitive recording material as claimed in claim 1 , which contains, as the activator, a sulfonate of a cycloaliphatic alcohol. 
     
     
       6. A heat-sensitive recording material as claimed in claim 1 , which contains, as the activator, a sulfonate of a saturated secondary aliphatic alcohol of 3 to 12 carbon atoms. 
     
     
       7. A heat-sensitive recording material as claimed in claim 1, which contains, as the color-producing substance, a diarylmethane, triarylmethane, fluorane, phenothiazine, xanthene, thioxanthene, spiropyran or acridine dye in the form of its leuco base or in its leuco-lactone form. 
     
     
       8. A heat-sensitive recording material as claimed in claim 1, wherein the heat-sensitive layer additionally contains a film-forming polymer as the binder. 
     
     
       9. A heat-sensitive recording material as claimed in claim 8, wherein the binder is polystyrene, polyvinyl chloride, polymethyl methacrylate or polyvinyl alcohol.